Television



March 9, 1943. c, GOLDMARK 2,313,062

TELEVISION Filed July 26, 1941 3 SheeQs-Sheet l INVENTOR Peter (T60621222479? ATTORNEYS March 9, 1943. p GQLDMARK j 2,313,062

TELEVISION Filed July 26, 1941 3 Sheets-Sheet 2 INVENTOR Peter C 'oZaman? A TTO RNEYJ March 9, 1943. P. c. GOLDMARK 2,313,062

TELEVISION Filed July 26, 1941 3 Sheets-Sheet 3 "54 g g INVENTOR Peter CGaZamarZ BY 214-41 W ATTORN EYS Patented Mar. 9, 1943 TELEVISION PeterGoldmark, New Canaan, Conn., assignor to Columbia Broadcasting System,Inc., New York, N. Y., a corporation of New York Application July 26,1941, Serial No. 404,168

6 Claims.

This invention relates to television scanning apparatus, particularly tofilm-scanning apparatus used in television transmitters. The inventionespecially relates to a method and apparatus for scanning film-frameareas of a continuously moving film at a field-scanning frequencydifferent from the film-frame frequency.

At the present time the televising of program material recorded on filmis of considerable practical importance. It is contemplated that forsome time at-least, ordinary sound-motion-picture film will be employedas well as sound motion pictures especially recorded for televisionpurposes. Present television standards for black and white pictures, inthe United States, require the transmission of images at the rate of 30pictures per second, double interlaced. Thus the component fieldseansions are produced at the rate of 60 fields per second. In motionpicture practice, however, sound films are recorded and projected at therate of 24 pictures per second. To coordinate these two differentstandards, the present widely adopted practice is to scan successivefilm frames alternately two and three times at the rate of 60 fieldscansions per second. In

the frames scanned three times, the third scansion is a duplicate of oneof the other two. Thus, 24 frames of the film are transmitted in asecond but 60 field scansions are employed for doing so, therebyproperly coordinating the motion picture and television standards.

Intermittent film scanners have been employed which operate inaccordance with this system by moving the film intermittently at thalternate rates of 30 frames per second and 20 frames per second. Also.film scanners operating under this system but employing a continuouslymoving film have been disclosed in my co-pending application Serial No.210,607, filed May 28, 1938. As explained in that application, thescanning pattern at the film must be displaced with respect to the pathof travel of the film for successive field seansions to compensate forfilm movement and cause successive field scansions to register withrespective film-frame areas. Accordingly, that application disclosesinter alia the use of five fixed lenses or five fixed mirrors, or asingle mirror intermittently moved to each of five positions to yieldthe proper scanning.

In other systems heretofore suggested, a plurality of stationary prisms,particularly wedgeshaped prisms, have been employed.

At the present time considerable attention has been directed toward thetransmission and reproduction of television images in natural color.

films of the Kodachrome" or Technicolor type in which the images on thefilm are in natural colors. In one type system found to givesatisfactory results the color images are successively scanned in aplurality of different primary colors. With a continuously moving film,this requires a displacement of the scanning pattern with respect to thepath of travel of the film to compensate for the movement of the filmbetween successive scansions of the same film frame areas.

The apparatus of application Serial No. 210,607, supra, may be employedin such color systems as well as in black and white systems. However,the present invention provides a different apparatus in which therequired displacement of the scanning pattern at the film is produced ina difi'erent manner. The specific embodiment described hereinafter isdesigned for the transmission of film in natural colors. However, itwill be understood that the apparatus can be employed in thetransmission of black and white pictures, the required modificationsbeing in part pointed out hereinafter and in part obvious to those inthe art. a

In accordance with the invention, an optical system includin a rotatabledisk having a plurality of transparent segments spaced therearound ispositioned between a continuously moving film and a scanning device sothat as the disk rotates the segments are successively interposed in thepath of the image rays between the film and the scanning device. Thetransparent segments have plane parallel faces and are inclined in thelongitudinal axial plane of the image rays so that they produce a shiftof the image rays in the longitudinal direction. It is contemplated thatthe faces of the segments will be parallel to the plane of the disk andthe disk inclined in the longitudinal axial plane of the image rays, thethicknesses and refractive indices of the segments being correlated withthe angle of inclination to produce a plurality of shifts of the imagerays. Ordinarily it is contemplated that each segment will remain inoperation throughout a field-scanning period and the shift produced bysuccessive mainder of the optical system to render a plurality of spacedfixed areas in the path of travel of the film successively comugate withsubstantially the same area of the scanning device.

It is preferred to employ segments having substantially the samerefractive index, and obtain diiferent shifts by making the segments ofdifferent thicknesses. However, as will be shown hereinafter, therefractive index also affects the degree of shift so that a combinationof different thicknesses and different refractive indices, or the samethicknesses and different refractive lndlces in a suitable case, may beemployed if desired.

.While a single image-shifting disk may be employed, in accordance witha preferred embodiment of the invention a pair of disks inclined inopposite directions in the longitudinal axial plane of the image raysare employed. These disks are rotated in substantial synchronism and thecombined thicknesses of each cooperating pair of segments is selected toyield substantially equal optical lengths of path for different pairs.In this manner, aberrations due to different lengths of glass and airpaths in successive pairs of segments are avoided.

The use of a rotating disk inclined in the longitudinal axial plane ofthe image rays and havingplane parallel segments spaced therearoundpossesses many advantages. Even though the disk turns through aconsiderable angle while a given segment is operating, the shift remainssubstantially constant in magnitude and direction. Only one set oflenses need be employed in conjunction with the disk, so that the sameset of lenses functions for all the field scansions. Suitable lenses ofdesired quality are commonly available. The aperture of the lens systemcan be made relatively large so that adequate light with a source ofrelatively small intensity can be obtained. Moreover, successivesegments of the rotating member occupy substantially the same positionin the optical path during the intervals they are in operation, therebyfacilitating the design of a suitably corrected optical system. Also,the use of a separate rotating shutter is unnecessary.

The invention will be more fully understood by reference to the specificembodiment illustrated in the drawings and the following descriptionthereof.

In the drawings:

Fig. 1 is a diagrammatic view in a longitudinal (vertical) plane offilm-scanning apparatus employing a pair of oppositely inclinedimage-shifting disks;

Fig. 2 is a detail of the disks: in a lateral (horizontal) plane;

Fig. 3 is a face view of the heat-shielding disk l6 of Fig. 1;

Figs. 4 and 5 are face and side views, respecin which the image shiftsfunction to render different fixed areas in the path of travel of thefilm conjugate to the same area of the scanning device;

Fig. 11 is a diagram illustrating the longitudinal and lateral axialplanes; and

two lenses.

Fig. 12 is a view of a pair of disks having segments arranged for filmscanning at the rate of 24 film frames and 60 fields per second.

Referring to Fig. 1, a film ll carried on sprockets I2 is fedlongitudinally with continuous uniform motion by motor l3. A' source oflight, here shown as an arc l4 and mirror I5, is positioned toilluminate the film ll. Between the light source and the film ispositioned a heatshielding disk IE, described more fully hereinafter.

A lens I! is positioned to render a film in the film-feeding mechanismconjugate to a selected intermediate image plane I8. As here shown, thelens I! is formed by two common lenses placed back to back, with a maskl9 having an opening 20 therein placed between the Since the twocomponent lenses cooperate to form an image on the film l l at the planeIS, the two component lenses may be considered simply as a lens.

A second 1ens 22 is positioned to render the intermediate image plane I8conjugate to the scanning device 23. This scanning device may be of anysuitable type. The embodiment of Fig. l employs a non-storage tube knownas an Image dissector tube. Lens 22 focuses an image at plane l8 ontothe photoelectric cathode 24 of the scanning tube; An electron image isthereby emitted from cathode 24 and is caused to sweep across thecollecting anode 25 by the horizontal deflecting coil 26, verticaldefiecting coil 21, and their associated saw-tooth oscillators. Whenconvenient. the scanning pattern may be considered as formed at thecathode 24.

A rotatable color filter disk 2|, driven by motor I3, is positioned inthe path of rays to the scanning device. It is advantageously placednear the intermediate image plane I8 but slightly removed therefrom sothat any imperfections in the filters will not be sharply focused at thescanning device. If desired, thedisk may be placed at any suitable pointbetween the source of light and the scanning device. The disk 2i has aplurality of different colored filter segments which are successivelyinterposed in the path of the light rays.

In the path of the light rays from the film to the scanning device ispositioned a pair of rotatable disks 28 and 28'. The disks could bedesigned to rotate in either direction, but it is preferable to havethem rotate so that the dividing lines between segments traverse theimage rays in the direction of low frequency scanning, therebypermitting relatively short segments and small disks to be employed.These disks are advantageously placed near the intermediate image planeis and on each side thereof as illustrated. In these positions thecross-section of the image rays at each disk is relatively small, thuspermitting segments of relatively short circumferential length, andhence a small disk, to be employed without cutting off marginal rays.Also, the boundaries between segments are fairly sharply defined at theintermediate image plane i8, so that as the disk rotates the change fromone operating segment to the next takes place quickly as the boundarybetween them traverses the image area.

Since both disks cannot be placed exactly at the intermediate imageplane iii, the longitudinal length of the opening 20 in mask i9 may beselected to cut off marginal rays which would pass through segmentsadjacent the correct operating segment and impinge on por- As shown moreclearly in Figs. 4 and 5, each disk comprises a plurality of transparentsegments 28a, 28b, 28c, 28d and 28a, spaced around the disk. Thesegments are of different thicknesses in accordance with principleshereinafter described; Actually, in the specific embodiment shown, thereare four glass segments and one open air segment 28a. As will beexplained hereinafter, 28a might also be a segment of glass, andtherefore the open air segment may be considered as a transparentsegment of zero thickness. For convenience, segment 28a is representedby a double line, but will be understood to be entirely open.

The boundaries between segments are advantageously at an angle withrespect to the axis of the disk, as shown in Fig. 5, so that theboundaries are substantially parallel to the axial ray as they traversethe image rays. This causes the boundaries to be more'sharpiy defined atthe image plane l8 and results in a quick change from one operatingsegment to the next as the boundary traverses a given area of the imageplane l8.

As shown in Figs. 1 and 2, the disks are positioned so that as theyrotate the segments thereof are interposed in the path of the imagerays, the boundaries traversing the rays in the longitudinal direction.The disks are driven simultaneously and in phase by suitable means, hereshown as motor l3, so that cooperating pairs of segments traverse theimage fieldat the same time. Fig. 6 is a development of one of thedisks, and shows the relative thicknesses of the segments.

The disks specifically illustrated contain five segments, in order toobtain the proper sequence of shifting hereinafter described inconnection with Fig. 10. However, it will be understood that the numberof transparent segments may be selected in view of the film-frame speed,field frequency of scanning, and the particular relationships selected,so as to produce the desired amounts and sequence of shifts.

From Figs. 1 and 2 it will be seen that the two disks are inclined inthe longitudinal axial plane of the image rays in opposed directions.

. The term longitudinal axial plane will be understood by reference toFig. 11, which shows the longitudinal axial plane 42 and a lateral plane43, shown with respect to the film H. The axis of the optical system isrepresented by line 44, and the longitudinal axial plane is a planeextending longitudinally of the film and containing the axis 44. In Fig.l the optical elements are arrangedin alignment. If desired, the axis ofthe system may be bent through 90 degrees or in any other desired mannerin order to secure a more compact or convenient arrangement. In suchcase it will be understood that the longitudinal axial plane will alsobe bent. In any case, the disks are so inclined of refraction a.

angle a, however, the displacement is directly as to produce a shift ofthe image rays in the longitudinal direction. 1

The principles involved in the shifting of the image by the transparentsegments is illustrated in Fig. 8. Fig. 8a illustrates a transparentsegment 28a (open) of the left-hand disk of Fig. 1,.

cooperating with a segment 28a of the righthand disk. A ray of light 3|passes through the transparent segment 28a and of course is undeviated.The ray 3| impinges on segment 28a, however, at an angle a with thenormal 32 to the surface. In accordance with well known principles ofoptics, in passing through the glass plate the ray of light 3| undergoesan upward displacement at given by the following formula:

d=TXsin a l- (j) 1 SiH (1 As indicated by the formula, the displacementd is a function of the thickness T of the glass plate, the angle ofincidence a and the index For a given ,a and a given proportional to thethickness T. For the scanning system described hereinafter in connection.withFig. 10, these factors are correlated to produce a displacement 11equal to %H', where H 'is theheight of a film frame as magnified orreduced by the optical system I], as will be understood.

. Fig. 8b shows the pair of cooperating segments 28b and 28'b. Here, thelight ray 3| is displaced downwardly by the segment 28b, since thesegment is of opposite inclination to segment 28a of Fig. 8a. The rayemerges from segment 28bparallel to its initial direction but displacedtherefrom. It then impinges on the segment 28'b at the same angle a asbefore, and is displaced upwardly. For the scanning sequence of' Fig.10,it is desired that the over-all displacement in Fig. '8b be one-halfthat of Fig. 8a. Furthermore, in order to avoid aberrations it isdesirable that the lengths of path in glass be the same in 3b as in 8a.This may be obtained by using a thickness /.;T for segment 28b and %Tfor 28fb. This results in an initial displacement downwardly of H' bythe first segment and an upward displacement of H by the second segment,thereby yielding an over-all displacement of H' in the upward direction.In Fig. 8c the two segments are of the same thickness but of oppositeinclination, thus yielding an over-all displacement of zero. In Fig. 8dthe initial segment 28d has a thickness %T and the second segment 28'dhas a thickness /.;T. This is the reverse of Fig. 8b and results in adownward displacement of 15H. In Fig. 8c the thicknesses are the reverseof Fig. 8a, yielding an over-all downward displacement of H'.

It will be noted that in each of the figures of Fig. 8 the combinedthicknesses of each cooper-- ating pair of segments is equal. However,the relative thicknesses of different cooperating pairs are selected soas to "produce different longitudinal shifts of image rays.

' Fig. 9 shows a transparent segment 28a formed of two pieces of glassof slightly different refractive index so as to provide a suitablecorrection. Segments thus corrected may be employed for all the glasssegments, or may be confined to only the thicker ones, as desired.

Referring now to Fig. 10, a scanning sequence is illustrated which isparticularly adapted for the scanning of color motion picture film atthe rate of 24 film frames per second and 120 fields per second.Successive fields are scanned in successive primary colors, red, greenand blue. It is contemplated that interlaced scanning will be employed.For example, the double-interlaced scanning sequence shown in Fig. 9 ofmy copending application Serial No. 355,840, filed September 7, 1940.may be employed. However, it will be understood that a different numberof colors and a. different number of interlaces may be employed ifdesired.

In Fig. 10 a fragment of film II is illustrated in the positions whichit occupies at the beginnings of successive field-scanning periods I,II. III, IV, V and I. With a film movement of 24 film frames per secondand 120 field scansions per second, field scansions take place duringthe interval that one film frame moves past a given point. Also, duringeach field scansion the film moves a. distance of A5H. It is preferredto scan the film longitudinally in a direction opposite to the filmmovement. Hence, the scanning pattern 36 at the film need be only H inheight, the movement of the film during the field scanning periodsupplying the remaining H to scan completely the film-frame area. Ifdesired, however, the apparatus could be designed to scan longitudinallyin the direction of movement. As indicated, the scanning patternconsists of lines extending laterally of the film and displacedlongitudinally thereof, forming a two-dimensional scanning pattern.

At the end of field scansion V the lower filmframe area 35 has beenscanned in 5 field scansions, and at the beginning of the nextfieldscanning period I the upper film frame area 31 occupies the samerelative position in the filmfeeding mechanism that the lower frameoccupied at the beginning of the first field scansion I.

The vertical lines 36a, 36b, 36c, 36d, 36c represent the length of thescanning pattern in the longitudinal direction, and the successivedisplacements thereof by an amount AH at the beginnings of successivefield scanning periods. These patterns are actually formed in the plane38, which is the plane of the path of travel of the film. The lines 36a,36b, 36c, 36d, 36c are shown separated from plane 38 for clearness ofillustration. The scanning areas represented by lines 36a, 36b, 36c,35d, 36e are fixed with respect to the path of travel of the film, andare spaced with respect to each other. It will be understood that theterm spaced applied to these areas includes the condition where theareas actually overlap, as is the case in Fig. 10.

The scanning areas 36a, 36b, 35c, 36d, 36s are rendered conjugate to theintermediate image plane I8 by lens II, as explained in connection withFig. l. The respective positions at plane I8, prior to shifting, areindicated by the vertical lines 36a, 36b',36c', 36d and 36c. The lines39 represent rays from the extremities of the respective areas. Theimage-shifting disks 28, 28' at the intermediate plane I8 shift theimage for successive field-scanning periods in the manner describedhereinbefore. This causes all the intermediate images of the scanningareas to coincide successively at the area 4|, also considered to be inplane [8, but shown displaced therefrom for clearness of illustration.Area 4| is then rendered conjugate to the plane 24 of the scanningdevice by lens 22.

In the actual embodiment of Fig. l the image shifting disks 28, 28' arenot exactly at the intermediate image plane l8, but are on either sidethereof. Therefore the image rays are shifted by the segments of disk 28before they reach the intermediate plane, and are further shifted by thesegments of disk 28' after they pass the intermediate plane. However,for ease in understanding the principles of operation, the simplifiedarrangement of Fig. 10 has been resorted to.

From the foregoing explanation it will be understood that theimage-shifting disks function to render a plurality of spaced fixedareas in the path of travel of the film successively conjugate tosubstantially the same area of a selected image plane 24. A scanningpattern at plane 24, provided by a suitable scanning device, need not bedisplaced longitudinally even though it is required to register withlongitudinally displaced areas in the path of travel in the film. Thedisks perform this funcion. However, if desired, the usual slightdisplacement of the scanning pattern for interlaced scanning may beemployed, as described in application Serial No. 210,607

' mentioned hereinbefore.

As before mentioned, the heat disk [6 shown in Figs. 1 and 3 is providedto prevent the heat from the projection source from adversely affectingthe film ll. With a scanning device of the non-storage type, such as theimage dissector shown, it is necessary to illuminate a line of the filmonly at the time that particular line is being scanned. The heat disktherefore contains slots 4la, 4|b, Me, 41d and Me, extending throughequal central angles, one for each of the scanning areas 36a, 36b, 36c,36d and 366. For the specific case illustrated, slots Ma and Me arecontinuations of each other. For a different specific embodiment thismight not be true. The width of the slots is such as to expose only afraction of the film frame to light from the projection source at anyone time. In the limiting case this might be one line, but to avoiddifiiculties due to curvature of the slots and the necessity ofmaintaining very accurate phase relationships, the slots are preferablymade wide enough to cover a number of scanning lines at a time.

Slot 41a operates during field scansion I. The beginning of the slotexposes the lower lines of film frame 36 (Fig. 9) and as the heat diskrotates, slot Ma progresses toward the top of the film frame to exposeareas as they are scanned. Since the film frame moves downward /5Hduring the film scanning period, the end of the slot need be displacedradially only %H with respect to the beginning thereof. Successive slotsoperate in similar manner during successive field scanning periods. Thebeginning and end of slot Mb is displaced inwardly a radial distance ofH with respect to the beginning and end of slot 4|a, to compensate forthe displacement of the continuously moving film during the firstscansion period. Slots 4 l0, Md and Me are displaced inwardly in asimilar manner to expose filmframe 36 during respective scansion periodsIII, IV and V. At the end of period V, slot Ma again comes intooperation to expose the succeeding film-frame 31 during field-scansion Iof that film frame, etc.

As before noted, the number of segments of the image displacing disksand the thicknesses thereof may be selected to produce the displacementsrequired by the scanning system employed. Fig. 12 illustrates a pair ofdisks suitable for use in conjunction with a film scanning apparatus inwhich film continuously moving at the rate of 24 film frames per secondis scanned at the rate of 60 field scansions per second. As shown inapplication Serial No. 210,607, supra, such a coordination of standardsmaybe obtained by shifting the scanning pattern at the film through +%H,0, %H, H and V5H. These displacements may be effected by arranging thesegments in Fig. 1 in order around the left hand disk with thicknesses0, T, T, %T and %T;

and cooperating segments on the right hand disk with thicknesses T, T,0, /{1 and /;T, where a thickness T is selected to yield a displacementof %H.

For any other scanning system, the thicknesses and order may be suitablychosen to yield the desired displacements.

It will be understood that in the specific embodiments described hereinthe image of the film at the scanning device is continuously moving,since the lenses I! and 22 are fixed with respect to the scanningdevice. However, the shifts produced by the disks cause longitudinallycorresponding parts of the same and successive film-frame areas to beconjugate to the same area of the scanning device at correspondinginstants in their respective longitudinal scanning periods.

In the specific embodiment described herein the film images areprojected to the scanning device, which is the preferred arrangement,but it will be understood that a luminous scanning pattern could beformed by the scanning device, for

example, on the screen of a cathode-ray tube,

and the rays passed through the disks to the film film frames changeslightly due to shrinkage, etc.,

thereby rendering the displacements produced by the several pairs ofsegments of the disks slightly inexact, lenses l1 may be adjusted tochange the magnification between film and plane 18 so as to restore theimages at plane I8 to the size for which the disks were designed. Ifdesired. however, the intermediate image plane could be dispensed with,with more or less success.

It will be understood that the present invention is not limited to themere details of construction and arrangement of the parts disclosed,since many modifications may be made by those in the art withoutdeparting from the spirit and scope of the invention.

I claim:

1. In television, apparatus for scanning an object field which comprisesan optical system for focusing an image of said object field at aselected plane, a pair of rotatable disks each having a plurality oftransparent segments spaced therearound, said disks being positionednear said selected plane and mounted so that as the disks rotatecooperating pairs of segments are successively interposed in the path ofthe 'image rays, said plurality of segments having plane parallel facessubstantially parallel to the planes of rotation of the respective disksand field scanning at'a speed such that each cooperating pair ofsegments operates substantially throughout at least one field-scanningperiod, the combined effective thicknesses of each cooperating pair ofsegments being selected to yield substantially equal optical lengths ofpath and the relative thicknesses of different cooperating pairs beingdifferent so as to-produce a plurality of diiferent shifts of the imagerays in the low-frequency direction.

2. Television film-scanning apparatus which comprises a film-feedingmechanism for feeding a film longitudinally with continuous uniformmotion, an optical system for rendering a plurality of spacedsubstantially fixed areas in the path of travel of the film successivelyconjugate to substantially the same area of a selected image surface,said optical system including a pair of rotatable disks each having aplurality of transparent segments spaced therearound, saiddisks beingpositioned-between said film and said image surface so that as the disksrotate the segments thereof are successively interposed in ,to yieldsubstantially equal optical lengths of path and the relative thicknessesand refractive indices being correlated with the angles of inclinationso that different cooperating pairs produce difierent longitudinalshifts of the image rays, and a scanning device positioned and adaptedto provide a scanning pattern at said selected image surface.

3. Television film-scanning apparatus which comprises a film-feedingmechanism for feeding a film longitudinally with continuous uniformmotion, a lens positioned to render an area of said film conjugate to aselected intermediate image plane, a scanning device, a second lenspositioned to render said intermediate image plane conjugate to saidscanning device, a pair of rotatable disks each having a plurality oftransparent segments spaced therearound, one of said disks beingpositioned on each side of said intermediate image plane and mounted sothat as the disks rotate said segments are successively interposed inthe path of the image rays, said plurality of segments having planeparallel faces substantially parallel to the planes of rotation of therespective disks and said planes of rotation being inclined in thelongitudinal axial plane of the image rays in opposed directions so thatsegments of respective disks displace the image rays in respectivelyopposite longitudinal directions, means for rotating the disks insubstantial synchronism, the combined thicknesses of each cooperatingpair of segments being substantially equal and the relative thicknessesof different cooperating pairs being diiferent so as to proscanningdevice.

scanning film-frame areas at a field frequency different from thefilm-frame frequency which comprises a film-feeding mechanism forfeeding a film longitudinally with continuous uniform motion andselected film-frame frequency, a lens positioned to render an area ofsaid film conjugate to a selected intermediate image plane, a-

scanning device for scanning areas of said film in two dimensions at afield-scanning frequency substantially different from said film-framefrequency, a second lens positioned to render said intermediate imageplane conjugate to said scanning device, a pair or rotatable disks eachhaving a plurality of transparent segments of different thicknessesspaced therearound with plane parallel faces substantially parallel tothe planes of rotation of the respective disks, one of said disks beingpositioned on each side of said intermediate image plane and mounted sothat as the disks rotate said segments are successively interposed inthe path of the image rays, said planes of rotation being inclined inthe longitudinal axial plane of the image rays in opposed directions sothat segments of respective disks displace the image rays: inrespectively opposite longitudinal directions, means for rotating thedisks in substantial synchronism at a speed such that cooperatinsegments traverse the image rays at substantially field-scanningfrequency, the combined thicknesses of each cooperating pair of segmentsbeing substantially equal to yield substantially equal optical lengthsof path and the relative thicknesses being correlated with therefractive indices and angles of inclination to longitudinally shift theimage rays by amounts sufficient to compensate for film movement andcause longitudinally corresponding parts of the film-frame areas to beconjugate to substantially the same area of the scanning device atcorresponding instants in their respective longitudinal scanningperiods,

5. In a color television system, apparatus for scanning an object fieldwhich comprises an optical system for focusing an image of said objectfield at a selected intermediate image plane, a pair of rotatable diskseach having a plurality of transparent segments spaced therearound, saiddisks being positioned one on each side of and near said intermediateimage plane, and mounted so that as the disks rotate cooperating pairsof segments are successively interposed in the path of the image rays,said plurality of segments having plane parallel faces substantiallyparallel to the planes of rotation of the respec-.

tive disks, said planes of rotation being inclined in opposed directionsso that segments of respective disks displace the image rays in oppositelow-i'requency directions, a rotatable colorfilter disk disposed betweensaid pair of rotatable disks and adjacent said intermediate image plane,a scanningdevice positioned to receive the color-filtered image raysafter said displacing and adapted to scan the image in two dimensions atfield-scanning frequency, means for rotating the paired disks insubstantial synchronism with the field scanning at a speed such thateach cooperating pair of segments operates substantially throughout atleast one field-scanning period, the relative thicknesses of differentcooperating pairs being different so as to produce a plurality ofdifferent shifts of the image rays in the low-frequency direction.

6. In a television system, apparatus for scanning an object field whichcomprises an optical system for focusing an image of said object fieldat a selected intermediate image plane, a pair of rotatable disks eachhaving a plurality of transparent segments spaced therearound, saiddisks being positioned one on each side of and near said intermediateimage plane, and mounted so that as the disks rotate cooperating pairsof segments are successively interposed in the path of the image rays,said plurality of segments having plane parallel faces substantiallyparallel to the planes of rotation of the respective disks, said planesof rotation being inclined in opposed directions so that segments of therespective disks displace the image rays in opposite low-frequencydirections, a scanning device positioned to receive the image rays aftersaid displacing and adapted to scan the image in two dimensions atfield-scanning frequency, means for rotating the disks in substantialsynchronism with the field scanning at a speed such that eachcooperating pair of segments operates substantially throughout at leastone field-scanning period, the combined effective thicknesses of eachcooperating pair of segments being selected to yield substantially equaloptical lengths of path, and the relative thicknesses of difierentcooperating pairs being different so as to produce a plurality ofdifferent shifts of the image rays in the lowfrequency directaion.

PETER. C. GOLDMARK.

